Various perf fixes for loading tutorials

[riknoll]

Fixing a couple perf issues:

1. We call stopSimulator several times when loading a project/tutorial. Each time this is called, it causes two setStates on app.tsx even if the simulator is already stopped. Added some code to prevent that
2. Removed a query selector in TutorialContainer

Also fixed an exception I noticed while debugging this; the VerticalResizeContainer was subscribing/unsubscribing events in an unsafe way. Also, it was doing a query selector in the render function which is never safe to do; always put dom manipulation inside a useEffect hook so it's guaranteed to run after the dom has rendered.

[thsparks]

Thank you!